Pulse delay circuits



'Oc t. 28,1 947. .ML THMAN T 2,429,844

PULSE DELAY CIRCUITS Filed Jan. 15, 1945 2 Sheets-Sheet 1 IOO v.

VOLTAGE INVENTORS. FlG.2.. MAX I. ROTHMAN WALTER H. NEIMAN ATTORNEY Oct. 28, 1947. M. R'OTHMANTET AL 2,

PULSE DELAY CIRCUITS Filed Jan. 1:5, 1945 2 Sheets-Sheet 2 IIIIHIITLEFELL'F v ll-l INVENTORS. MAX I. ROTHMAN ATTORNEY 7 [WALTER H.NE|MAN a M.

Patented Oct. 28, 1947 PULSE DELAY CIRCUITS Max I. Rothman, Hollis, and Walter H. Neiman, Sea Clifi, N. Y.; said Rothman assignor of his right to the Government of the United States of America, as represented by the Secretary of War Application January 13, 1945, Serial No.. 572,718

3 Claims.

This invention relates, to impulse energy-operated devices and more particularly to an arrangement for producing substantially fixed delay for all applied impulses. The invention is contemplated to have particular utility in impulse energy-operated systems as are employed for the radio location of aircraft and other mobile bodies where fixed or adjustably controllable delays may be desirable.

It is an object of this invention to provide improved means for efiectively delaying a series of impulses recurring periodically or in a more or less random manner, a predetermined amount for each impulse thereof.

Another object of this invention is to provide a device of the above type which will yield delayed impulses of sharply defined form.

Yet another object of this invention is to provide impulse delay apparatuscharacterized by a high degree of stability and not susceptible to voltage fluctuations in thepower supply associated therewith.

A further object of this invention is to provide impulse delay apparatus with relatively flexible means for adjusting the effective delay thereof..

For a better understanding of the invention together with other objects and further features of novelty thereof, reference is had to thefollowing specification. taken in; connection with the accompanying drawing wherein like parts are indicated by like, reference numerals. The scope of the invention will be pointed out in, the accompanying claims. In the accompanying drawing,

Figure 1 is a schematic circuit diagram of, a preferred embodiment of the present invention.

Figure 2A is a schematic circuit diagram illustrative of a specific feature of the invention while Figure 2B shows the discharge characteristics curve of a resistance-capacitance network included in Figure 2A and,

Figure 3 is a schematic circuit diagram of another preferred embodiment of the present invention.

Referring now to the drawing and more particularly to Figure 1, one preferred embodiment of the invention is shown including a grid-controlled gas-filled tube ID, a diode vacuum tube I I and a pair of triode vacuum tubes I2 and I3. For purposes of simplicity, tube'heaters are omitted from the diagram. Plate voltage for tubes I0, I], I2 and I3 is provided by B. battery I4.

'Shunted across battery I4 is a bleeder network comprising in series connection, variable resistor I5, potentiometer I6 and variable resistor I1.

Grid bias for gas-filled tube In is furnished by C battery I8, the voltage thereof being sufficient to bias the tube I0 beyond cut-ofi whereby it is normally nonconductive, The anodes of gasfilled tube [0 and diode II are tied together and connected to. the positive terminal of battery I4 through condenser I9 shunted by resistor 20. The cathode of diode II is connected to the sliding arm of potentiometer I6 through the primary winding of a step-up transformer 2I. Since initially the anode of diode II is at positive potential'in respect to the cathode, the tube is normally conductive.

The impulses to be delayed are applied to the input terminals 22 where they are imposed upon the grid circuit of gas-filled tube I0 through capacitor 23. These impulses are of the type shown by form 24 and have a magnitude and a polarity with respect to the grid of tube I9 sufiicient to overcome the cut-off bias impressed thereon by battery I8, thereby firing said tube.

When gas-filled tube II) is fired, the internal impedance thereof is greatly diminished so that condenser I9 in the platecircuit becomes charged to substantially the voltage of battery I4. Thereupon, the charged condenser I9 proceeds to discharge. through. resistor 20 at a ratedetermined by the. time constant of the network. Since the polarity of charged condenser I9 is negative in respect to the anodes of tubes I0 and II, gasfilled tube I0 is extinguished and diode II is rendered nonconductive.

The effect of the discharge action of condenser I9 upon diode II, and the circuit components associated therewith, may be understood more clearly by referring to Figures 2A and 2-B wherein only the active components inconnection with diode II are shown. It will be assumed, for purposes of explanation, that battery I4 furnishes a potential of volts. Consequently, at the instant of maximum. charge, condenser I9 will also store 100 volts. It will be assumed further that the sliding, of potentiometer I6 is adjusted so that the cathodeof diode I I is set at a 50-vo1t tap. It may readily be seen that inasmuch as the negative terminal of the fully charged condenser I9 is connected to the anode of diode II,. the over-all potential on the anode is 50 volts negativein respect to the. cathode. Thus, when condenser I9 is in the condition of full charge, diode II is rendered nonconductive causing the field in the primary of transformer 2| to collapse thereby inducing a surgeof energy in thesecondary winding thereof. A condenser 25 is connected between ground and one side of a priversus time characteristics curve of condenser I9 2 and resistor 20 is shown. At maximum charge the condenser potential is 100'vo1ts. When at a point along the exponential discharge curve, the charge of the condenser is reduced to 50 volts. it will be seen by referring to Figure 2-A that the plate voltage on diode II is now zero in respect to the cathode. If the condenser charge further diminishes beyond the 50-volt point, the plate becomes positive in respect to the cathode and the diode II is rendered conductive causing a surge of current through the primary winding of transformer 2I in a direction opposite to the flow occurring when the tube is rendered nonconductive. Thus, a second pulse is produced in the secondary of transformer 2I spaced from the first pulse for a time determined by the nonconduction period of diode II. It is evident if the cathode of diode II were connected to a tap exceeding 50 volts, conduction would occur at a later interval in the discharge curve of condenser 20, whereas if the cathode were connected to a tap providing less than 50 volts, diode II would be rendered conductive at an earlier interval in the discharge period.

The voltage applied to the cathode of diode I I may be adjusted by Varying either resistor I5, potentiometer I6, or resistor II. By varying the cathode voltage, the spacing between the first and second pulse yielded in the secondary of transformer 2! may be controlled. In practice, the settings of variable resistors I5 and I! preferably are fixed at points whereby the desired range of spacing between the first and second pulse may be effected solely by the adjustment of potentiometer I6.

It is to be noted that if B battery I 4 is supplanted by a power supply of poor regulation, voltage fluctuations in the output thereof will not influence the predeterminedspacing between the first and second pulse. For example, if the voltage of the power supply rises from 100 to 120 volts, the full charge of condenser I9 will likewise rise to 120 volts, while the cathode voltage secured at the arm of potentiometer I6 would then be 60 volts, so that the ratio between cathode and plate voltage in diode II would remain undisturbed. As is well known, the characteristics of an exponential condenser discharge are such that condenser will discharge a constant percentage of its voltage in a given time. Consequently, irrespective of its fully charged voltage, which in this instance is either 100 volts or 120 volts, the time at which the condenser is dis charged to a 50-volt point in the first case, or a 60-volt point in the second case, is identical since in both cases they are at the half-Way discharge level. Diode H would then be rendered conductive at the same instant when employing a 120- volt supply as when battery I9 provided 100 volts. Accordingly, within the operating voltage values of tubes II) and II, Voltage supply fluctuations will not alter the spacing between the first and second pulses yielded in the output of transformer 2I.

Referring again to Figure 1, it has been demonstrated thus far that for each impulse applied to the grid of gas-filled tube III there is obtained in the secondary of transformer 2|, as illustrated by form 2 I a first pulse appearing substantially at the instant diode II is rendered nonconductive by the charging of condenser I9, and a second pulse, spaced a predetermined interval from the first pulse and opposed in polarity thereto, which appears when diode II again becomes conductive at a selected point during the discharge of condenser I9.

The second or delayed pulse is employed to trigger a blocking oscillator, of novel construction, including triodes I2 and I3 which generates a single sharply defined pulse for each triggering pulse. The circuit of the blocking oscillator is designed so that the first pulse effects no triggering action.

Plate voltage-for triode I2 is secured through resistor 26 while plate voltage for triode I3 is obtained through resistor 21. The ohmic value of resistor 26 is relatively high as compared to resistor 21, hence the voltage on the anode of triode I2 is relatively low compared to that of triode I3. The cathodes of triodes I2 and I3 are tied together and connected to ground through resistor 28. The grid of triode I3 is connected to ground througha grid leak 29 having an extremely high resistance. The grid of triode I2 is connected to cathode through the secondary of transformer 2I .having a fairly small directcurrent resistance. It may be seen that the grid of triode I3 is negative in respect to cathode to a degree determined by the voltage drop across resistor 28, while the grid of triode I2 is substantially at cathode potential. Initially, triode I2 is conductive whereas triode I3 is biased to cut-off.

The secondary winding of transformer 2I is directly connected to the grid and cathode of triode I2 in a manner whereby the first pulse induced therein applies a positive voltage to the grid, while the second or delayed pulse applies a negative voltage to the grid. When a positive voltage appears on the grid of triode I 2, plate current flow increases, causing a corresponding drop in plate voltage as a result of the IR drop developed across resistor 25 which, in turn, imposes a negative voltage upon the grid of triode I3 through coupling capacitor 30. Inasmuch as triode I3 is normally nonconductive, the negative voltage appearing on the grid effects no further diminution in current fiow. Accordingly, the blocking oscillator is not triggered by positivegoing pulses. j I

When, however, a negative pulse is applied to the grid of triode I2, the flow of current therein is decreased resulting in a rise in plate voltage whereupon a positive surge is applied to the grid of triode I3 rendering said tube conductive. With current flowingthrough triode I3, the voltage drop across resistor 28-is augmented, thereby effectively decreasing the flow of current through triode I2. The reductionin current flow in triode I2 further increases the voltage on the plate thereof causing an increasein the positive surge applied to the grid of triode I3 through capacitor 30 resulting in a repetition of the efiect above described. This regeneration is permitted to continue only for a, single cycle because of the voltagedrop developedacross grid leak 29 when grid current is drawn upon"theapplication of a positive voltage on the grid of triode I3. The grid leak 29 impresses anegative bias on the grid of triode l3 which blocks any further oscillation beyond the first cycle for a period determined by the time constant ofcapacitor 30 and grid leak 29. The oscillator reverts to its initial condition until again'excited by a negative triggeringpulse. Accordingly, for each negative triggering pulse applied to the grid of triode 12 there is generated in triode I3 a pulse which is negative going in the plate circuit and positive going at the cathode. The former pulses are made available at terminals 3! and the latter at terminals 32.

It is sometimes desirable in a delay circuit operating in accordance with the principles underlying this invention to employ tubes of the hard vacuum type in preference to the gas-filled tube Ill shown in Figure 1. It has been found that an error is sometimes introduced in the operation of the delay circuit due to variations in the deionization time of a gas-filled tube when exposed to radio frequency energy. Since the delay circuit may be employed in conjunction with and in proximity to pulse-echo transmitters, a second embodiment of the invention is disclosed in Figure 3 wherein only non-gaseous tubes are included whose operation is not influenced by radio frequency energy.

Referring now to Figure 3, the delay circuit entails the use of three diode vacuum tubes 33, 34 and 35 and a blocking oscillator employing a pair of triode vacuum tubes 33 and 31. Sincethe blocking oscillator is identical both in design and operation with that disclosed in connection with Figure 1 including tubes l2 and l3, it will not be necessary to review the explanation of its theory of operation. Plate voltage for tubes 33 to 37 is furnished by a B battery 33. Shunted across battery 38 is a bleeder series network consisting of variable resistor 39, potentiometer 4|] and variable resistor 4|. The plate of diode 33, the cathode of diode 34, and the plate of diode 35 are tied together and connected to one side of the secondary of a step-up transformer 42 through a condenser 44 shunted by a resistor 45. The other side of the secondary of transformer 42 is connectedto the cathode of diode as. The plate of triode 34 is directly connected to ground While the cathode of diode 35 is connected to the sliding arm of potentiometer 40 through the primary of a step-up transformer 43.

The incoming impulses to be delayed are applied to terminals 46 where they are fed to the primary of transformer 42. The polarity of incoming impulses is made such whereby the impulses induced in the secondary of transformer 42 apply a positive potential to the plate of diode 33 with respect to the cathode thereof which renders diode 33 conductive thereby charging condenser 44. The pulses in the secondary of transformer 42 as shown by form 41 are of such amplitude as to exceed in potential the voltage provided by battery 33. When condenser 44 is charged, its negative terminal is connected to the plates of diodes 33 and 35 and the cathode of diode 34. If the charge on condenser 40 exceeds the potential of battery 45, the cathode of diode 34 becomes negative in respect to the plate thereof and thetube conducts to ground. Thus, regardless of the magnitude of the voltage applied to condenser 43, the charge thereon can never exceed the voltage of battery 38 since beyond that point tube 34 conducts to ground. For that reason the amplitude of applied impulses may vary without affecting the maximum charge stored by condenser 45.as long as the minimum impulse exceeds in magnitude the voltage of battery 38.

Condenser 44 proceeds to discharge through resistor 45 and diode 35 is rendered nonconductive since the potential at the plate is now neg- 6 ative in respect to the cathode. When diode 35 is rendered nonconductive the collapsing field in the primary of transformer 43 induces a surge of energy in the secondary 'thereof which is shaped into a fairly well defined pulse form by the presence of capacitor 43 connected between one side of the primary of transformer 43 and ground, the combination serving as a pulse forming network. At the point inthe exponential discharge curve of condenser 44 where the plate of diode 35 becomes positive in respect to cathode, the diode is again rendered conductive and a current surge flows in the primary of transformer 43 which induces a second pulse in the secondary thereof spaced from the first pulse and opposed in polarity thereto as shown by form 49.

The secondary of transformer 43 is connected between the grid and cathode of triode 36 in a manner whereby the second or delayed pulse applies a negative potential to the grid thereby triggering a blocking oscillator in the manner described hereinabove in connection with Figure 1.. Negative going delayed pulses of the type shown by form 53 are obtained at terminals 5| coupled to the plate circuit of tube 31 while positive going delayed pulses as shown by form 5| are made available at terminals 52 coupled to the cathode circuit of tube 31.

It will be seen that there has been disclosed relatively simple means for effectively delaying recurrent impulse energy. Although this delay is attained by generating new impulses for those applied, the arrangement shown has the advantage of producing extremely sharp and well defined impulses at the output waves. If some passive network had been employed to obtain cult to attain a well defined delayed pulse, the

larger the delay. If it be desired to produce delayed impulses of the same form as those applied to the input, the delayed impulses produced by the circuit shown may be used to synchronize a wave generator having suitable shaping means and by monitoring input pulse shapes and shaping the newly generated pulse shapes to conform thereto, the effect of flexibly adjustable delay is produced With no apparent distortion.

Although the delay has been disclosed to be adjustably controllable by controlling the voltage applied to the cathode of diode II, it is to be understood that the delay adjustment may be effected by other means. For example, the ohmic value of resistor 25 shunting condenser IS in Figure 1 or resistor 45 shunting condenser 44 in Figure 3 may be adjusted thereby varying the delay of the circuits. While this invention has been described as being particularly adaptable to the delaying of time-modulated impulse energy, it is clear that it may be equally applicable to systems employing frequency modulation impulses, that is, impulses whose frequency of recurrence is modulated in accordance with a given signal.

Although throughout the above specification and in the annexed claims reference has been made to the type of energy which was fed to the apparatus as impulse energy, it is to be understood that this term embraces impulses in a broad aspect, that is, not only the relatively short abrupt form as shown by form 24 in Figure 1 but also any type of electrical fluctuation.

While there have been described what are at present considered preferred embodiments of the invention, it will be obvious to those skilled in the art thatvarious changes and modifications may bemade therein without departing from the invention, and it is, therefore, aimed in the appendedclaims to cover all such changes and modifications as fall within the true spiritand scope of the invention.

, We claim: V

1. Apparatus for producing output impulses delayed a predetermined amount of time with respect to input triggering impulses comprising a source of direct-current potential having an intermediate tap, a resistance-capacitance parallel network having one terminal connected to the positive pole of said source, a diode discharge device having an anode and a cathode, means connecting said anode to the other terminal of said network, means connecting said cathode to .said intermediate tap whereby said diode is initially conductive, means responsive to a triggering impulse and independent of its duration to couple momentarily the negative pole of said source to said other terminal of said network whereby said network is instantly charged to substantially the full potential of said source, thereby rendering said diode nonconductive for a period determined by the time constant of said network, and means to develop an output impulse at the moment said network is discharged to the level at which said diode is again rendered conductive, said means for developing an impulse comprising a step-up transformer having a primary winding and a secondary winding, said primary winding being interposed between said cathode and said intermediate tap, a capacitor connected between said intermediate tap and said negative pole, said capacitor in combination with said primary winding being adapted to act as an impulseforming network, whereby an output impulse is induced in said secondary winding at the moment said diode is rendered conductive or nonconductive.

2. Apparatus for producing output impulses delayed a predetermined amount of time with respect to input triggering impulses comprising a source of direct-current potential having an intermediate tap, a resistance-capacitance parallel network having one terminal connected to the positive pole of said source, a diode discharge device having an anode and a cathode, means connecting said diode anode to the other terminal of said network, means connecting said diode cathode to said intermediate tap whereby said diode is initially conductive, a gas tube having an anode, a cathode, and a control grid, said gas tube anode being connected to said other terminal of said network, said gas tube cathode being connected to the negative pole of said potential source, means for applying a triggering impulse to said gas tube grid and independent of the duration of said triggering impulse to fire said tube, thereby instantly charging said network to substantially the full potential of said source whereby thepotentialat the anode ofsaid gas tube decreases to an extent where said gas tube is extinguished and said diode is rendered nonconductive for a period'determined by the time constant of said network, and means for developing an output impulsive at the moment said network is discharged to the level at which said diode is again rendered conductive.

BHApparatus for producing output impulses delayed a predetermined amount of time with respect to input impulses comprising a source of direct-current potential having an intermediate tap, a resistance-capacitanceparallel network having: one, terminal oonnected to the positive pole ofsaid source, a diode discharge device having an anode and a cathode, means connecting said diode anode" to theotherterminal of said network, a step-up transformer having a primary winding and a secondary winding, one side of said primary winding being connected to said intermediate tap, the other side of said primary winding being connected to said diode cathode whereby said diode is initially conductive, a gas tube having an. anode,,afcathode and 'a control grid, said gas tubje anode being connected to said diode anode, said gas'tube cathode being connected to the negative pole of said potential source, means for applying a triggering impulse to said gas tube grid, and independent of the duration of said triggering impulse, to fire said gas tube, thereby instantly charging said network to substantially the full potential of said source whereby the potential at the anode of said gas tube decreases to an extent where said gas tube is extinguished and said diode is rendered nonconductive for a period determined by the time constant of said network, a capacitor connected between said intermediate tap and said negative pole, said capacitor in combination with said primary winding of saidtransformer being adapted to act as an impulse-forming network whereby an output impulse is induced in said secondary Winding at the moment said diode is rendered conductive or nonconductive, and means for adjusting the position of said intermediate tap in said source of potential whereby the time delay of said output impulse with respect to said triggering impulse may be adjusted.

MAX 1. ROTHMAN WALTER H. NEIMAN.

REFERENCES CITED The following references are of record in the file of this patent: 

